1. Field of the Invention
The present invention relates to an air bag system for a motor vehicle, and more particularly to an air bag system for a motor vehicle having an air bag module capable of rapidly inflating by a small quantity of inflating gas for an air bag.
2. Description of the Prior Art
A variety of air bag apparatuses for motor vehicles have been proposed hitherto. A conventional air bag apparatus for a motor vehicle generally includes an inflatable air bag and a collision sensor for sensing the collision of the motor vehicle to generate a collision sensing signal. Also, the conventional air bag apparatus includes an electronic control unit (hereinafter referred to as "ECU") for receiving the collision sensing signal from the collision sensor to control the operation of the air bag, and an inflator for injecting gas or air into the inflatable air bag in accordance with an air bag expansion triggering signal from the ECU to expand the air bag.
FIG. 4 illustrates a schematic view of the constitution of the conventional air bag apparatus. As shown in FIG. 4, if a shock is applied to a car body by the collision with another vehicle or object while the vehicle is moving along a road, the vehicle's collision is monitored by a collision sensor 10 mounted to the forefront of the vehicle. Collision sensor 10 generates the collision sensing signal and supplies it to an ECU 20 when the shock against the car body exceeds a preset shock value required for inflating an air bag 40. ECU 20 determines whether or not the collision sensing signal is received from collision sensor 10 to provide the air bag expansion triggering signal to an inflator 30. Once the air bag expansion triggering signal is provided, inflator 30 injects an inert gas such as nitrogen N.sub.2 or argon Ar, or air into inflatable air bag 40 to instantaneously inflate air bag 40. Consequently, the passenger in the vehicle can be protected from colliding with a structural part of the vehicle by the inflated air bag 40.
In the conventional air bag apparatus operated as above, since an inflation gas of high temperature and high pressure produced by the explosive combustion of a pyrotechnic material and a gas generating material being an ignitable material included in the inflator is instantaneously supplied into the folded air bag having a volume of about 60 to 120 L to inflate the air bag, large quantities of pyrotechnic material and gas generating material are required for a perfect expansion of the air bag. Moreover, at the moment of air bag 40 expands, the driver or the passenger who contacts air bag 40 might get burnt by the inflation gas of high temperature and high pressure and might get secondary shock by the high pressure of air bag 40. Besides, after expanding the air bag, the inflation force of the air bag is degraded resulting from the decreased pressure of the inflation gas.
U.S. Pat. No. 5,186,492 issued to Eric W. Wright on Feb. 16, 1993 discloses an air bag module capable of being employed in an air bag apparatus for a motor vehicle. The disclosed air bag module comprises a reaction device, a container including a cover fixed to the reaction device, an air bag disposed substantially in the container and an inflator coupled to the container. In this air bag module, the air bag can be efficiently fixed to the container and can be disposed in the container using relatively few parts. Besides, the air bag module can be mounted advantageously in a limited space available in a steering wheel. However, although the assembly thereof is simple and the establishment thereof is advantageous, since the air bag module described in the Eric W. Wright patent still employs the conventional air bag and inflator, the above-mentioned problems still remain.
Meantime, the air bag installed to a front passenger seat beside a driver's seat in the motor vehicle should have a capacity larger than the air bag implemented to the driver's seat by approximately 2.5 times since the physical features of the passenger occupying the front passenger seat vary more than the driver occupying the driver's seat. In other words, the passenger occupying the front passenger seat just beside the driver's seat differs from a child to an adult and probably has a relatively unstable posture as compared with the driver. Therefore, in order to safely protect the passenger on the front passenger seat from an accident, the air bag mounted to the passenger's compartment must have a capacity greater than that of the air bag mounted to the driver's compartment. As the result, the air bag having a capacity greater than that of the air bag for the driver's compartment has been typically mounted to the passenger's front compartment.
An inflator devised for generating gas of a great volume for supplying gas having a larger volume into the air bag of the relatively great capacity to obtain a desired inflating force has been employed.
U.S. Pat. No. 5,219,178 issued to Hirokazu Kobari et al. on Jun. 15, 1993 discloses an air bag inflation gas generator which includes a substantially circular cylinder formed with a gas exhaust in the middle portion thereof. Two combustion chambers formed by separating members are provided to both ends of the circular cylinder. In addition, a cylindrical end filter is installed coaxially with the circular cylinder within the center of the circular cylinder, middle filters are installed between the separating members and an end filter, and orifices directing the middle filters are formed. An object of the inflation gas generator constructed as above is for generating a combustion gas having a greater volume and for increasing the combustible surface area of gas generating materials to thereby adjust the expansion of the air bag in the optimum state.
The Hirokazu Kobari's generator can supply the combustion gas of the larger volume, but two combustion chambers and the plurality of filters are employed for generating the combustion gas of the larger volume. Consequently, the inflation gas generator is disadvantageous in that large quantities of pyrotechnic material and gas generating material are required, the construction is complicated and a high manufacturing cost is needed.
FIG. 5 illustrates an air bag module which has been employed in the conventional air bag apparatus. An air bag module 100 has a container 110, an air bag 40 disposed in container 110 and a cylindrical inflator 30 secured to container 110. Container 110 has a reaction device 120 and a cover 130 fastened to reaction device 120. Container 110 defines an internal cavity 112.
Air bag 40 generally having a volume of from 60 to 120 L is disposed substantially in internal cavity 112. A portion of air bag 40 is disposed between cover 130 and reaction device 120, and is secured to a retainer frame 48 located outside of container 110. The remaining portion of air bag 40 is disposed in internal cavity 112 of container 110.
Cover 130 is preferably made of a flexible plastic material. The inside of cover 130 has internal score lines 132 disposed in a predetermined configuration.
Inflator 30 is attached to container 110 after the container has been preassembled. Inflator 30 has a cylindrical outer housing 32. Cylindrical outer housing 32 has a plurality of gas dispensing nozzles 34. When a motor vehicle collides, gas dispensing nozzles 34 rapidly discharge inert gas such as nitrogen into a second internal cavity 114 in air bag 40 to expand air bag 40.
Generally, air bag 40 and inflator 30 are connected to reaction device 120. Reaction device 120 is connected to a structural part of a vehicle. Reaction device 120 includes a reaction plate 122 formed of sheet steel. Reaction plate 122 comprises a planar main body 124, a pair of spaced apart, arcuate bands 126, and a series of first flanges 128. A central opening 140 is formed in planar main body 124. Central opening 140 extends between arcuate bands 126. First flanges 128 are formed at the perimeter of planar main body 124, and extend substantially perpendicular to planar main body 124.
Four threaded shafts 142 (only two of them are shown) are used to couple air bag module 100 to the structural part of a vehicle. Threaded shafts 142 are integrally connected to and extend away from main body 124. First flange 128 extends rearward away from an external wall 116 of container 110.
Arcuate bands 126 form a cradle for receiving cylindrical inflator 30. When inflator 30 is properly aligned in the cradle formed by arcuate bands 126, a plurality of gas dispensing nozzles 34 formed cylindrical outer housing 32 of inflator 30 will be aligned with central opening 140 in main body 124 to direct gas discharged by inflator 30 through central opening 124 and into second internal cavity 114 of air bag 40. First flanges 128 positioned at the periphery of main body 124 is suitable to fix cover 130 to reaction plate 122.
Cover 130 is a cup-shaped member. Four second flanges 150 (only two of them are shown) are formed at the border of cover 130. Formed in second flanges 150 on cover 130 and first flanges 128 on reaction plate 122 are rivet holes 152 and 154, respectively. Rivet holes 152 and 154 are aligned with each other to enable rivets or other fasteners to be driven through the aligned holes to fasten cover 130 securely with reaction plate 122.
FIG. 6 illustrates air bag 40 in air bag module 100 illustrated in FIG. 5. Air bag 40 has a mouth 42. Mouth 42 defines an inlet opening through which gas is communicated with second internal cavity 114 in air bag 40. The air bag fabric is formed into a fabric tube 44 at mouth 42 of air bag 40. A retainer frame 48 comprises a continuous frame member 46 adapted to be disposed inside fabric tube 44.
The air bag fabric adjacent to fabric tube 44 is disposed between second flanges 150 on cover 130 and first flanges 128 on reaction plate 122, as illustrated in FIG. 5. The air bag fabric is fixed between first flanges 122 and second flanges 150 by fastening second flanges 150 on cover 130 and second flanges on reaction plate 122 together.
With the conventional air bag module 100 constituted as described above, since air bag 40 expands by rapidly injecting inflation gas of high temperature and high pressure into air bag 40 having a volume of about from 60 to 120 L, a large amount of pyrotechnic material and gas generating material is needed in order to accomplish a complete expansion of air bag 40. In addition, after the complete expansion of air bag 40, the inflation gas of high temperature and high pressure may burn a driver or a passenger who contacts air bag 40, and, further, the high pressure may apply a secondary shock to the driver or passenger. Besides, after the complete expansion of air bag 40, the expanding power of air bag 40 can be rapidly lowered due to the reduced pressure of the inflation gas.